Electrode-aligned selective epitaxy method for vertical power devices

Abstract

A method of forming trench electrode structures includes forming a first dielectric layer on a semiconductor substrate, forming a second layer above the first dielectric layer and forming an opening which extends through the second layer and the first dielectric layer to the semiconductor substrate such that part of the semiconductor substrate is uncovered. The method further comprises forming an epitaxial layer on the uncovered part of the semiconductor substrate, removing the second layer after forming the epitaxial layer and filling an open space formed by removing the second layer with an electrically conductive material. The electrically conductive material forms an electrode which is laterally surrounded by the epitaxial layer.

What is claimed is: 
     
       1. A method of forming trench electrode structures, the method comprising:
 forming a first dielectric layer on a semiconductor substrate; 
 forming a second layer above the first dielectric layer; 
 forming an opening which extends through the second layer and the first dielectric layer to the semiconductor substrate such that part of the semiconductor substrate is uncovered; 
 forming an epitaxial layer on the uncovered part of the semiconductor substrate; 
 removing the second layer after forming the epitaxial layer; and 
 filling an open space formed by removing the second layer with an electrically conductive material, the electrically conductive material forming an electrode which is laterally surrounded by the epitaxial layer. 
 
     
     
       2. The method of  claim 1 , wherein the first dielectric layer comprises oxide and the second layer is on the first oxide layer and comprises nitride. 
     
     
       3. The method of  claim 2 , further comprising:
 depositing a second oxide layer on the nitride layer, 
 wherein the opening extends through the second oxide layer, the nitride layer and the first oxide layer to the semiconductor substrate. 
 
     
     
       4. The method of  claim 3 , further comprising:
 depositing oxide along a bottom and sidewalls of the opening prior to depositing the epitaxial layer; 
 removing the oxide from the bottom of the opening prior to depositing the epitaxial layer and from at least an upper part of lateral sides of the epitaxial layer prior to filling the open space with the electrically conductive material such that at least the upper part of the lateral sides of the epitaxial layer is exposed; and 
 forming a gate dielectric on the exposed part of the lateral sides of the epitaxial layer prior to filling the open space with the electrically conductive material. 
 
     
     
       5. The method of  claim 1 , wherein the first dielectric layer comprises oxide and the method further comprises:
 depositing an electrically conductive layer on the first oxide layer; 
 depositing a second oxide layer on the electrically conductive layer; and 
 depositing a nitride layer on the second oxide layer, 
 wherein the nitride layer is the second layer, 
 wherein the opening extends through the nitride layer, the second oxide layer, the electrically conductive layer and the first oxide layer to the semiconductor substrate. 
 
     
     
       6. The method of  claim 5 , further comprising:
 forming a semiconductor layer above the epitaxial layer in the opening prior to removing the second layer, the semiconductor layer being doped oppositely as the epitaxial layer and having lateral sides which face the second layer. 
 
     
     
       7. The method of  claim 6 , further comprising:
 forming a gate dielectric on the lateral sides of the semiconductor layer after removing the second layer and prior to filling the open space with the electrically conductive material. 
 
     
     
       8. The method of  claim 5 , further comprising:
 depositing oxide along a bottom and sidewalls of the opening prior to depositing the epitaxial layer; 
 removing the oxide from the bottom of the opening prior to depositing the epitaxial layer and from at least an upper part of lateral sides of the epitaxial layer prior to filling the open space with the electrically conductive material such that at least the upper part of the lateral sides of the epitaxial layer is exposed; and 
 forming a gate dielectric on the exposed part of the lateral sides of the epitaxial layer prior to filling the open space with the electrically conductive material. 
 
     
     
       9. The method of  claim 1 , further comprising:
 depositing alternating layers of electrically conductive material and dielectric material above the first dielectric layer; and 
 depositing a nitride layer on an uppermost one of the dielectric layers, 
 wherein the nitride layer is the second layer, 
 wherein the opening extends through the nitride layer, the alternating layers of electrically conductive material and dielectric material and the first oxide layer to the semiconductor substrate, 
 wherein the electrically conductive material that fills the open space forms a gate electrode, 
 wherein each layer of electrically conductive material below the gate electrode forms a field electrode which is vertically spaced apart from the other field electrodes and the gate electrode by the alternating layers of dielectric material. 
 
     
     
       10. The method of  claim 9 , further comprising:
 forming a semiconductor layer above the epitaxial layer in the opening prior to removing the second layer, the semiconductor layer being doped oppositely as the epitaxial layer and having lateral sides which face the second layer. 
 
     
     
       11. The method of  claim 10 , further comprising:
 forming a gate dielectric on the lateral sides of the semiconductor layer after removing the second layer and prior to filling the open space with the electrically conductive material. 
 
     
     
       12. The method of  claim 1 , wherein the first dielectric layer comprises oxide and the second layer is on the first oxide layer and comprises polysilicon. 
     
     
       13. The method of  claim 12 , further comprising:
 depositing oxide along a bottom and sidewalls of the opening prior to depositing the epitaxial layer; 
 removing the oxide from the bottom of the opening prior to depositing the epitaxial layer and from lateral sides of the epitaxial layer prior to filling the open space with the electrically conductive material such that the lateral sides of the epitaxial layer is exposed; and 
 forming a gate dielectric on the exposed lateral sides of the epitaxial layer prior to filling the open space with the electrically conductive material. 
 
     
     
       14. The method of  claim 13 , further comprising:
 replacing the electrically conductive material with new electrically conductive material in the open space after forming the epitaxial layer. 
 
     
     
       15. The method of  claim 14 , further comprising:
 replacing the gate dielectric with a new gate dielectric in the open space after forming the epitaxial layer and prior to replacing the electrically conductive material. 
 
     
     
       16. The method of  claim 1 , further comprising:
 depositing oxide along a bottom and sidewalls of the opening prior to depositing the epitaxial layer; and 
 removing the oxide from the bottom of the opening prior to depositing the epitaxial layer. 
 
     
     
       17. The method of  claim 16 , further comprising:
 thermally oxidizing the semiconductor substrate after the opening is formed and prior to depositing the oxide. 
 
     
     
       18. The method of  claim 16 , further comprising:
 removing the oxide from lateral sides of the epitaxial layer prior to filling the open space with the electrically conductive material such that the lateral sides of the epitaxial layer are exposed; and 
 forming a gate dielectric on the exposed lateral sides of the epitaxial layer prior to filling the open space with the electrically conductive material. 
 
     
     
       19. The method of  claim 16 , further comprising:
 removing the oxide from an upper part of lateral sides of the epitaxial layer prior to filling the open space with the electrically conductive material such that the upper part of the lateral sides of the epitaxial layer is exposed and a lower part of the lateral sides of the epitaxial layer remains covered by the oxide; and 
 forming a gate dielectric on the exposed upper part of the lateral sides of the epitaxial layer prior to filling the open space with the electrically conductive material. 
 
     
     
       20. The method of  claim 1 , wherein the semiconductor substrate is a Si substrate and the epitaxial layer is a Si epitaxial layer.